Re: [PATCH 3/7] mm/hmm: fix race between hmm_mirror_unregister() and mmu_notifier callback

From: Balbir Singh
Date: Thu Aug 30 2018 - 10:14:53 EST

On Fri, Aug 24, 2018 at 03:25:45PM -0400, jglisse@xxxxxxxxxx wrote:
> From: Ralph Campbell <rcampbell@xxxxxxxxxx>
> In hmm_mirror_unregister(), mm->hmm is set to NULL and then
> mmu_notifier_unregister_no_release() is called. That creates a small
> window where mmu_notifier can call mmu_notifier_ops with mm->hmm equal
> to NULL. Fix this by first unregistering mmu notifier callbacks and
> then setting mm->hmm to NULL.
> Similarly in hmm_register(), set mm->hmm before registering mmu_notifier
> callbacks so callback functions always see mm->hmm set.
> Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
> Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
> Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx

Reviewed-by: Balbir Singh <bsingharora@xxxxxxxxx>